Of course you don't really know what you're doing. That's why you asked for help doing it. That's the whole meaning of the question. The error is not in the answerer assuming the asker doesn't know what he's doing, the error is in the asker treating the ability to ask the right question about the problem as a different category of ability than the one required to solve the problem, and so getting offended about the additional implication they don't have that former after admitting they don't have the latter.